U.S. patent number 7,666,511 [Application Number 11/888,213] was granted by the patent office on 2010-02-23 for down-drawable, chemically strengthened glass for cover plate.
This patent grant is currently assigned to Corning Incorporated. Invention is credited to Adam James Ellison, Sinue Gomez.
United States Patent |
7,666,511 |
Ellison , et al. |
February 23, 2010 |
Down-drawable, chemically strengthened glass for cover plate
Abstract
An alkali aluminosilicate glass that is chemically strengthened
and has a down-drawable composition. The glass has a melting
temperature less than about 1650.degree. C. and a liquidus
viscosity of at least 130 kpoise and, in one embodiment, greater
than 250 kpoise. The glass undergoes ion exchange at relatively low
temperatures to a depth of at least 30 .mu.m.
Inventors: |
Ellison; Adam James (Painted
Post, NY), Gomez; Sinue (Corning, NY) |
Assignee: |
Corning Incorporated (Corning,
NY)
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Family
ID: |
40027805 |
Appl.
No.: |
11/888,213 |
Filed: |
July 31, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080286548 A1 |
Nov 20, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60930808 |
May 18, 2007 |
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Current U.S.
Class: |
428/426; 501/72;
501/70; 501/69; 501/68; 501/66; 501/65; 501/55; 501/53 |
Current CPC
Class: |
C03B
17/06 (20130101); C03C 21/002 (20130101); C03C
3/085 (20130101); C03C 3/091 (20130101); C03C
3/087 (20130101); Y02P 40/57 (20151101); Y10T
428/315 (20150115) |
Current International
Class: |
B32B
17/06 (20060101); C03C 3/076 (20060101) |
Field of
Search: |
;501/53,55,65,66,68,69,70,72 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3212612 |
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Oct 1983 |
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DE |
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1116699 |
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Feb 2006 |
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EP |
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1212123 |
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Nov 1970 |
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GB |
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2335423 |
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Sep 1999 |
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GB |
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1-167245 |
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Jun 1986 |
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JP |
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3454242 |
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Oct 2003 |
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JP |
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3465642 |
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Nov 2003 |
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JP |
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Primary Examiner: Blackwell; Gwendolyn
Attorney, Agent or Firm: Santandrea; Robert P. Schaeberle;
Timothy M.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 60/930,808, filed May 18, 2007.
Claims
The invention claimed is:
1. An alkali aluminosilicate glass, the glass comprising: 64 mol
%.ltoreq.SiO.sub.2.ltoreq.68 mol %; 12 mol
%.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %, and
wherein the glass has a liquidus viscosity of at least 130
kpoise.
2. The glass according to claim 1, wherein the glass is
down-drawable.
3. The glass according to claim 1, wherein the glass is
substantially free of lithium.
4. The glass according to claim 1, wherein the glass is ion
exchanged.
5. The glass according to claim 4, wherein the glass, when ion
exchanged, has a surface compressive stress of the glass of at
least about 200 MPa.
6. The glass according to claim 4, wherein the glass, when ion
exchanged, has a surface compressive layer having a depth of at
least about 30 .mu.m.
7. The glass according to claim 1, wherein the glass has a liquidus
viscosity of at least 250 kpoise.
8. The glass according to claim 1, wherein the glass has a
thickness ranging from about 0.3 mm up to about 3 mm.
9. The glass according to claim 8, wherein the glass has a
thickness ranging from about 0.3 mm up to about 1.5 mm.
10. The glass according to claim 9, wherein the glass has a warpage
of less than about 0.5 mm, as determined for a 300 mm.times.400 mm
sheet.
11. The glass according to claim 10, wherein the warpage is less
than about 0.3 mm.
12. The glass according to claim 1, wherein the glass is a cover
plate.
13. The glass according to claim 12, wherein the glass is a cover
plate for a mobile electronic device.
14. The glass according to claim 1, wherein the glass is slot drawn
or fusion drawn.
15. A lithium-free glass having a surface compressive stress of at
least about 200 MPa, a surface compressive layer having a depth of
at least in a range from about 30 .mu.m up to about 100 .mu.m, and
a thicknessof at least about 0.3 mm.
16. The lithium-free glass according to claim 15, wherein the
compressive stress is at least about 600 MPa, the depth of surface
compressive layer is at least 40 .mu.m, and the thickness is in a
range from about 0.7 mm up to about 1.1 mm.
17. The lithium-free glass according to claim 15, wherein the glass
comprises 64 mol %.ltoreq.SiO.sub.2.ltoreq.68 mol %; 12 mol
%.ltoreq.Na.sub.2.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %; (Na.sub.2O+B.sub.2O.sub.3)
--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %, and
wherein the glass has a liquidus viscosity of at least 130
kpoise.
18. The lithium-free glass according to claim 17, wherein the glass
has a liquidus viscosity of at least 250 kpoise.
19. The lithium-free glass according to claim 15, wherein the glass
has a thickness ranging from about 0.3 mm up to about 3 mm.
20. The lithium-free glass according to claim 19, wherein the glass
has a thickness ranging from about 0.3 mm up to about 1.5 mm.
21. The lithium-free glass according to claim 15, wherein the glass
is a cover plate.
22. The lithium-free glass according to claim 15, wherein the glass
is a cover plate for a mobile electronic device.
23. The lithium-free glass according to claim 15, wherein the glass
has a warpage of less than about 0.5 mm, as determined for a 300
mm.times.400 mm sheet.
24. The lithium-free glass according to claim 15, wherein the
warpage is less than about 0.3 mm.
25. The lithium-free glass according to claim 15, wherein the
lithium-free glass is fusion drawn or slot drawn.
26. A mobile electronic device, the mobile electronic device
comprising an alkali aluminosilicate glass cover plate, the glass
cover plate comprising: 64 mol %.ltoreq.SiO.sub.2.ltoreq.68 mol %;
12 mol %.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %, and
wherein the glass has a liquidus viscosity of at least 130
kpoise.
27. The mobile electronic device according to claim 26, wherein the
glass cover plate is substantially free of lithium.
28. The mobile electronic device according to claim 26, wherein the
glass cover plate is ion exchanged.
29. The mobile electronic device according to claim 28, wherein the
glass cover plate, when ion exchanged, has a surface compressive
stress at a surface of the glass of at least 200 MPa.
30. The mobile electronic device according to claim 28, wherein the
glass cover plate, when ion exchanged, has a compressive surface
layer having a depth of at least about 30 .mu.m.
31. The mobile electronic device according to claim 26, wherein the
glass cover plate has a liquidus viscosity of at least 250
kpoise.
32. The mobile electronic device according to claim 26, wherein the
glass cover plate has a thickness ranging from about 0.3 mm up to
about 3 mm.
33. The mobile electronic device according to claim 32, wherein the
glass cover plate has a thickness ranging from about 0.3 mm up to
about 1.5 mm.
34. The mobile electronic device according to claim 32, wherein the
glass cover plate has a warpage of less than about 0.5 mm, as
determined for a 300 mm.times.400 mm sheet.
35. The mobile electronic device according to claim 34, wherein the
warpage is less than about 0.3 mm.
36. The mobile electronic device according to claim 26, wherein the
glass is fusion drawn or slot-drawn.
37. An alkali aluminosilicate glass cover plate, the cover plate
comprising: 64 mol %.ltoreq.SiO.sub.2.ltoreq.68 mol %; 12 mol
%.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol %
.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO +SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %, and
wherein the glass has a liquidus viscosity of at least 130
kpoise.
38. The cover plate according to claim 37, wherein the cover plate
is substantially free of lithium.
39. The cover plate according to claim 37, wherein the cover plate
is ion exchanged.
40. The cover plate according to claim 39, wherein the cover plate,
when ion exchanged, has a surface compressive stress at a surface
of the glass of at least about 200 MPa.
41. The cover plate according to claim 39, wherein the cover plate,
when ion exchanged, has a compressive surface layer having a depth
of at least about 30 .mu.m.
42. The cover plate according to claim 37, wherein the cover plate
has a liquidus viscosity of at least 250 kpoise.
43. The cover plate according to claim 37, wherein the cover plate
has a thickness ranging from about 0.3 mm up to about 3 mm.
44. The cover plate according to claim 43, wherein the cover plate
has a thickness ranging from about 0.3 mm up to about 1.5 mm.
45. The cover plate according to claim 43, wherein the cover plate
has a warpage of less than about 0.5 mm, as determined for a 300
mm.times.400 mm sheet.
46. The cover plate according to claim 45, wherein the warpage is
less than about 0.3 mm.
47. The cover plate according to claim 37, wherein the glass is
fusion drawn or slot-drawn.
Description
TECHNICAL BACKGROUND
The invention relates to an alkali aluminosilicate glass. More
particularly, the invention relates to a high strength, down-drawn
alkali aluminosilicate glass. Even more particularly, the invention
relates to a high strength, down-drawn alkali aluminosilicate glass
for use as a cover plate in mobile electronic devices.
Mobile electronic devices, such as personal data assistants, mobile
or cellular telephones, watches, laptop computers and notebooks,
and the like, often incorporate a cover plate. At least a portion
of the cover plate is transparent, so as to allow the user to view
a display. For some applications, the cover plate is sensitive to
the user's touch. Due to frequent contact, such cover plates must
have high strength and be scratch resistant.
The touch sensitive screens of the latest such devices are
typically chemically-strengthened, ion-exchangeable "soda-lime"
type glasses. These are frequently complicated compositions
consisting not only of Na.sub.2O (soda), CaO (lime) and SiO.sub.2
(silica), but also include several other oxides such as MgO,
Li.sub.2O, K.sub.2O, ZnO, and ZrO.sub.2. These glasses are
compatible with large-scale sheet glass manufacturing via
floatation on a tin metal bath, but cannot be formed by methods,
particularly down-draw processes such as fusion draw and slot draw
processes, that are more traditionally associated with precision
sheet glass. This is because liquidus temperatures of such soda
lime glasses are too high--and their viscosities at the liquidus
temperature too low to be compatible with fusion or slot draw
processing.
SUMMARY
The present invention provides an alkali aluminosilicate glass that
is capable being chemically strengthened by ion exchange and
exhibits a composition which can be down-drawn into sheets. The
glass has a melting temperature of less than about 1650.degree. C.
and a liquidus viscosity of at least 130 kpoise and, in one
embodiment, greater than 250 kpoise. The glass can be ion exchanged
at relatively low temperatures and to a depth of at least 30
.mu.m.
Accordingly, one aspect of the invention is to provide an alkali
aluminosilicate glass having a liquidus viscosity of at least 130
kpoise. The glass comprises: 64 mol %.ltoreq.SiO.sub.2.ltoreq.68
mol %; 12 mol %.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%<Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %.
Another aspect of the invention is to provide lithium-free glass
having a compressive stress of at least 200 MPa, a depth of layer
of at least 30 microns, and a thickness of at least 0.3 mm.
Yet another aspect of the invention is to provide a mobile
electronic device comprising an alkali aluminosilicate glass cover
plate having a liquidus viscosity of at least 130 kpoise. The glass
cover plate comprises: 64 mol %.ltoreq.SiO.sub.2.ltoreq.68 mol %;
12 mol %.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %.
Still another aspect of the invention is to provide an alkali
aluminosilicate glass cover plate for a device. The glass cover
plate has a liquidus viscosity of at least 130 kpoise and
comprises: 64 mol %.ltoreq.SiO.sub.2.ltoreq.68 mol %; 12 mol
%.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %.
These and other aspects, advantages, and salient features of the
present invention will become apparent from the following detailed
description, the accompanying drawings, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of a mobile electronic device having a cover
plate comprising an alkali aluminosilicate glass.
DETAILED DESCRIPTION
In the following description, like reference characters designate
like or corresponding parts throughout the several views shown in
the figures. It is also understood that, unless otherwise
specified, terms such as "top," "bottom," "outward," "inward," and
the like are words of convenience and are not to be construed as
limiting terms. In addition, whenever a group is described as
comprising at least one of a group of elements and combinations
thereof, it is understood that the group may comprise any number of
those elements recited, either individually or in combination with
each other. Similarly, whenever a group is described as consisting
of at least one of a group of elements or combinations thereof, it
is understood that the group may consist of any number of those
elements recited, either individually or in combination with each
other. Unless otherwise specified, a range of values includes both
upper and lower limits of the range.
Referring now to FIG. 1, it will be understood that the
illustration is for the purpose of describing a particular
embodiment of the invention and is not intended to limit the
invention thereto.
An alkali aluminosilicate glass (also referred to herein as a
"glass") is provided. The glass has a liquidus viscosity of at
least 130 kpoise. As used herein, "liquidus viscosity" refers to
the viscosity of a molten glass at the liquidus temperature,
wherein the liquidus temperature refers to the temperature at which
crystals first appear as a molten glass cools down from the melting
temperature, or the temperature at which the very last crystals
melt away as temperature is increased from room temperature. The
glass comprises the following oxides, the concentrations of which
are expressed in mole percent (mol %):
64.ltoreq.SiO.sub.2.ltoreq.68; 12.ltoreq.Na.sub.2O.ltoreq.16;
8.ltoreq.Al.sub.2O.sub.3.ltoreq.12;
0.ltoreq.B.sub.2O.sub.3.ltoreq.3; 2.ltoreq.K.sub.2O.ltoreq.5;
4.ltoreq.MgO.ltoreq.6; and 0.ltoreq.CaO.ltoreq.5. In addition, 66
mol %.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %.
Exemplary compositions of the aluminosilicate glass are listed in
Table 1. Table 2 lists compositions that are outside the above
range and are deficient in at least one of melting temperature,
durability, and/or liquidus viscosity.
TABLE-US-00001 TABLE 1 Representative compositions. Example 1 2 3 4
5 6 7 8 9 Mol % SiO2 66.16 68 66 66.16 66 66 65.16 66.16 66.16
Al2O3 10.9 10.9 10.9 10.9 10.9 10.9 10.9 9.9 8.9 B2O3 0 0 0 0.62
0.62 0.62 0 0 0 Na2O 13.41 13.41 13.41 13.41 13.41 13.41 13.41
13.41 13.41 K2O 2.33 2.33 2.33 2.33 2.33 2.33 3.33 3.33 4.33 MgO
5.72 5.72 5.72 5.72 5.72 5.72 5.72 5.72 5.72 CaO 0.62 0.62 0.62 0 0
0 0.62 0.62 0.62 As2O3 0.25 0.41 0 0.25 0.41 0 0.25 0.25 0.25 Sb2O3
0 0 0.41 0 0 0.41 0 0 0 SnO2 0 0 0 0 0 0 0 0 0 Fe2O3 0 0 0 0 0 0 0
0 0 TiO2 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 properties
strain point 568 -- -- -- 573 -- -- -- 524 anneal point 618 -- --
-- 623 -- -- -- 571 softening point -- -- -- -- -- -- -- -- --
strain -- -- -- -- -- -- -- -- -- CTE 87.9 90.8 101.3 density
Viscosity T @ 200 p 1647 -- -- -- 1635 -- -- -- 1564 T @ 35 kp 1173
-- -- -- 1165 -- -- -- 1094 Liquidus internal 1025 -- -- -- 1020 --
-- -- 830 liq. Visc. 3.8E+05 -- -- -- 3.7E+05 -- -- -- 8.3E+06 Ion
Exchange time -- -- -- -- -- -- -- -- -- Average DOL (.mu.m) -- --
-- -- -- -- -- -- -- Average .sigma..sub.t (Mpa) -- -- -- -- -- --
-- -- -- Example 10 11 12 13 14 15 16 17 18 19 20 21 Mol % SiO2
66.16 66 66 66.16 66 64.16 66.16 66.02 64.745 66.15 64.45 65.7
Al2O3 10.9 10.9 10.9 8.9 10.9 10.9 8.9 10.94 10.97 8.943 9.695
10.92 B2O3 1.23 1.23 1.23 1.23 1.23 1.23 1.23 1.22 2.44 1.22 1.55
1.31 Na2O 13.41 13.41 13.41 13.41 13.41 13.41 13.41 13.46 13.49
13.44 14.14 13.- 43 K2O 2.33 2.33 2.33 4.33 2.33 4.33 4.33 2.355
2.36 4.285 3.785 2.33 MgO 5.72 5.72 5.72 5.72 5.72 5.72 5.72 5.5
5.52 5.66 5.44 5.86 CaO 0 0 0 0 0 0 0 0 0 0 0.82 0.06 As2O3 0.25
0.41 0 0.25 0 0.25 0.25 0.395 0.395 0.395 0.397 0.37 Sb2O3 0 0 0.41
0 0.41 0 0 0 0 0 0 0 SnO2 0 0 0 0 0 0 0 0 0 0 0 0 Fe2O3 0 0 0 0 0 0
0 0 0 0 0 0.01 TiO2 0 0 0 0 0 0 0 0 0 0 0 0.02 properties strain
point -- -- -- -- 559 550 529 -- -- -- -- 563 anneal point -- -- --
-- 609 598 575 -- -- -- -- 613 softening point -- -- -- -- -- -- --
-- -- -- -- 855 CTE 91.4 99.2 99.5 -- -- -- -- 2.4 density 2.463
2.454 2.436 -- -- -- -- 2.458 Viscosity T @ 200 p -- -- -- -- 1624
1595 1563 1635 1635 1594 1536 1633 T @ 35 kp -- -- -- -- 1150 1126
1086 1162 1162 1123 1069 1151 Liquidus internal -- -- -- -- 1050
725 825 865 870 800 800 1025 liq. Visc. -- -- -- -- 1.8E+05 3.3E+07
8.4E+06 1.7E+07 1.7E+07 3.7E+07 1.0- E+07 3.0E+05 Ion Exchange time
-- -- -- -- -- -- -- -- -- -- -- -- Average DOL (.mu.m) -- -- -- --
-- -- -- -- -- -- -- -- Average .sigma..sub.t -- -- -- -- -- -- --
-- -- -- -- -- (Mpa) Example 22 23 24 25 26 27 28 29 30 31 32 Mol %
SiO2 64.97 65.24 65.88 66.01 65.28 65.73 65.89 65.75 66.53 66.53
66.53 Al2O3 9 9.58 10.27 9.15 11.03 10.98 10.95 11.06 10.73 10.73
10.98 B2O3 2.34 1.69 0.63 1.07 1.32 1.32 0 0 0.5 1 0 Na2O 14.38
14.38 13.91 13.49 13.48 13.48 13.39 13.41 13.34 13.34 13.34 K2O
3.48 2.82 2.45 3.91 3.32 2.76 2.29 2.56 2.49 2.49 2.49 MgO 5.49
5.48 5.86 5.88 5.09 5.35 5.86 5.48 5.48 4.98 5.73 CaO 0.05 0.54
0.57 0.12 0.06 0.05 1.23 1.35 0.28 0.28 0.28 As2O3 0.28 0.25 0.4
0.36 0.01 0 0.37 0.38 0 0 0 Sb2O3 0 0 0 0 0.41 0.06 0 0 0 0 0 SnO2
0 0 0 0 0 0.23 0 0 0 0 0 Fe2O3 0.01 0.01 0.01 0.01 0.01 0.03 0.01
0.01 0 0 0 TiO2 0.02 0.02 0.01 0.02 0.02 0.02 0.02 0.02 0.65 0.65
0.65 properties strain point 516 529 559 532 544 562 579 576.9
anneal point 560 574 608 579 593 612 628 626 softening 757 786 843
814 838 862.8 858.5 point CTE density 2.461 2.460 2.455 2.457 2.453
2.46269 2.463 Viscosity T @ 200 p 1544 1559 1613 1586 1608 1639
1640 1636 T @ 35 kp 1058 1081 1131 1110 1129 1153 1168 1166
Liquidus internal 775 935 890 870 990 1025 980 liq. Visc. 9.7E+06
5.4E+05 4.9E+06 3.3E+06 4.1E+04 2.9E+05 1026862 Ion Exchange time
-- 8 8 -- -- -- -- -- -- -- -- Average -- 49 48 -- -- -- -- -- --
-- -- DOL (.mu.m) Average .sigma..sub.t -- 32.4 36.5 -- -- -- -- --
-- -- -- (Mpa) 33 34 35 36 37 38 39 40 41 42 Mol % SiO2 66.53 66.28
66.03 65.53 64.53 66.53 66.53 66.53 66.53 66.53 Al2O3 11.23 10.73
10.73 10.73 10.73 10.73 10.73 11.38 10.98 11.23 B2O3 0 0.25 0.5 1 2
0.5 1 0 0 0 Na2O 13.34 13.34 13.34 13.34 13.34 13.34 13.34 13.34
13.34 13.34 K2O 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.49
MgO 5.48 5.98 5.98 5.98 5.98 5.48 4.98 5.98 5.73 5.48 CaO 0.28 0.28
0.28 0.28 0.28 0.28 0.28 0.28 0.28 0.28 As2O3 0 0 0 0 0 0 0 0 0 0
Sb2O3 0 0 0 0 0 0 0 0 0 0 SnO2 0 0 0 0 0 0 0 0 0 0 Fe2O3 0 0 0 0 0
0 0 0 0 0 TiO2 0.65 0.65 0.65 0.65 0.65 0.65 0.65 0 0.65 0.65
properties strain point anneal point softening point CTE density
Viscosity T @ 200 p T @ 35 kp Liquidus internal liq. Visc. Ion
Exchange time -- -- -- -- -- -- -- -- -- -- Average DOL (.mu.m) --
-- -- -- -- -- -- -- -- -- Average .sigma..sub.t (Mpa) -- -- -- --
-- -- -- -- -- --
TABLE-US-00002 TABLE 2 Mol % 43 44 45 46 47 48 49 50 51 SiO2 64.16
66.16 66.16 64.16 66.16 63.79 64.24 66.58 67.16 Al2O3 10.9 10.9
10.9 10.9 10.9 10.92 10.96 11.03 10.98 B2O3 0 0 0 1.23 1.23 1.23
1.23 0 0 Na2O 13.41 12.41 11.41 13.41 11.41 13.54 13.48 13.27 13.41
K2O 4.33 3.33 4.33 4.33 4.33 4.335 3.73 2.5 2.56 MgO 5.72 5.72 5.72
5.72 5.72 5.72 5.92 5.56 5.54 CaO 0.62 0.62 0.62 0 0 0.06 0.07 0.07
As2O3 0.25 0.25 0.25 0.25 0.25 0.4 0.37 0.27 0.24 TiO2 0.61 0.61
0.61 0 0 0 0 0.66 0.67 Deficiency SiO.sub.2 +
Na.sub.2O--Al.sub.2O.sub.3 Na.sub.2O--Al.sub.2O.sub.3 SiO.sub.2 +
Na.sub.2O--Al.sub.2O.sub.3 SiO.sub.2 + B.sub.2O.sub.3 + SiO.sub.2 +
Na.sub.2O + K.sub.2O + Na.sub.2O + K.sub.2O + B.sub.2O.sub.3 + too
too B.sub.2O.sub.3 + too CaO too B.sub.2O.sub.3 + B.sub.2O.sub.3 +
MgO + B.sub.2O.sub.3 + MgO + CaO too low low CaO too low low CaO
too CaO + SrO CaO + SrO low melting melting low melting low too low
too low problem it poor T too T too poor T too poor poor melting T
melting T causes durability high high durability high durability
durability too high too high
The largest single constituent of the alkali aluminosilicate glass
is SiO.sub.2, which forms the matrix of the glass and is present in
the inventive glasses in a concentration ranging from about 64 mol
% up to and including about 68 mol %. SiO.sub.2 serves as a
viscosity enhancer that aids formability and imparts chemical
durability to the glass. At concentrations that are higher than the
range given above, SiO.sub.2 raises the melting temperature
prohibitively, whereas glass durability suffers at concentrations
below the range. In addition, lower SiO.sub.2 concentrations can
cause the liquidus temperature to increase substantially in glasses
having high K.sub.2O or high MgO concentrations.
When present in a concentration ranging from about 8 mol % up to
and including about 12 mol %, Al.sub.2O.sub.3 enhances viscosity.
At Al.sub.2O.sub.3 concentrations that are higher than this range,
the viscosity can become prohibitively high, and the liquidus
temperature may become too high to sustain a continuous down-draw
process. To guard against this, the glasses of the present
invention have a total concentration of alkali metal oxides (e.g.,
Na.sub.2O, K.sub.2O) that is well in excess of the total
Al.sub.2O.sub.3 content.
Fluxes are used to obtain melting temperatures that are suitable
for a continuous manufacturing process. In the aluminosilicate
glass described herein, the oxides Na.sub.2O, K.sub.2O,
B.sub.2O.sub.3, MgO, CaO, and SrO serve as fluxes. To satisfy the
various constraints on melting, it is preferable that the
temperature at 200 poise not be greater than 1650.degree. C. To
achieve this, the condition that
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO--Al.sub.2O.sub.3>10
mol % should be met.
Alkali metal oxides serve as aids in achieving low liquidus
temperatures, and low melting temperatures. As used herein, the
term "melting temperature" refers to the temperature corresponding
to a glass viscosity of 200 poise. In the case of sodium, Na.sub.2O
is used to enable successful ion exchange. In order to permit
sufficient ion exchange to produce substantially enhanced glass
strength, Na.sub.2O is provided in a concentration ranging from
about 12 mol % up to and including about 16 mol %. If, however, the
glass were to consist exclusively of Na.sub.2O, Al.sub.2O.sub.3,
and SiO.sub.2 within the respective ranges described herein, the
viscosity would be too high to be suitable for melting. Thus, other
components must be present to ensure good melting and forming
performance. Assuming those components are present, reasonable
melting temperatures are obtained when the difference between the
Na.sub.2O and Al.sub.2O.sub.3 concentrations ranges from about 2
mol % up to and including about 6 mol % (i.e., 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %).
Potassium oxide (K.sub.2O) is included to obtain low liquidus
temperatures. However, K.sub.2O--even more so than Na.sub.2O--can
decrease the viscosity of the glass. Thus, the total difference
between the sum of the Na.sub.2O and K.sub.2O concentrations and
the Al.sub.2O.sub.3 concentration should be in a range from about 4
mol % up to and including about 10 mol % (i.e., 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol
%).
B.sub.2O.sub.3 serves as a flux; i.e., a component added to reduce
melting temperatures. The addition of even small amounts (i.e.,
less than about 1.5 mol %) of B.sub.2O.sub.3 can radically reduce
melting temperatures of otherwise equivalent glasses by as much as
100.degree. C. While, as previously mentioned, sodium is added to
enable successful ion exchange, it may be desirable, at relative
low Na.sub.2O contents and high Al.sub.2O.sub.3 contents, to add
B.sub.2O.sub.3 to ensure the formation of a meltable glass. Thus,
in one embodiment, the total concentration of Na.sub.2O and
B.sub.2O.sub.3 is linked such that
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %. Thus,
in one embodiment, the combined concentration of SiO.sub.2,
B.sub.2O.sub.3, and CaO ranges from about 66 mol % up to and
including about 69 mol % (i.e., 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %).
When the total alkali metal oxide concentration exceeds that of
Al.sub.2O.sub.3, any alkaline earth oxides present in the glass
serve primarily as fluxes. MgO is the most effective flux, but is
prone to form forsterite (Mg.sub.2SiO.sub.4) at low MgO
concentrations in sodium aluminosilicate glasses, thus causing the
liquidus temperature of the glass to rise very steeply with MgO
content. At higher MgO levels, glasses have melting temperatures
that are well within the limits required for continuous
manufacturing. However, the liquidus temperature may be too
high--and thus the liquidus viscosity too low--to be compatible
with a down-draw process such as, for example, the fusion draw
process. However, the addition of at least one of B.sub.2O.sub.3
and CaO can drastically reduce the liquidus temperature of these
MgO-rich compositions. Indeed, some level of B.sub.2O.sub.3, CaO,
or both may be necessary to obtain a liquidus viscosity that is
compatible with fusion, particularly in glasses having high sodium,
low K.sub.2O, and high Al.sub.2O.sub.3 concentrations. Strontium
oxide (SrO) is expected to have precisely the same impact on
liquidus temperatures of high MgO glasses as CaO. In one
embodiment, the alkaline earth metal oxide concentration is thus
broader than the MgO concentration itself, such that 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %.
Barium is also an alkaline earth metal, and additions of small
amounts of barium oxide (BaO) or substitution of barium oxide for
other alkaline earths may produce lower liquidus temperatures by
destabilizing alkaline-earth-rich crystalline phases. However,
barium is considered to be a hazardous or toxic material.
Therefore, while barium oxide may be added to the glasses described
herein at a level of at least 2 mol % with no deleterious impact or
even with a modest improvement to liquidus viscosity, the barium
oxide content is generally kept low to minimize the environmental
impact of the glass. Thus, in one embodiment, the glass is
substantially free of barium.
In addition to the elements described above, other elements and
compounds may be added to eliminate or reduce defects within the
glass. The glasses of the present invention tend to exhibit 200
kpoise viscosities that are relatively high, between about
1500.degree. C. and 1675.degree. C. Such viscosities are typical of
industrial melting processes, and in some cases melting at such
temperatures may be required to obtain glass with low levels of
gaseous inclusions. To aid in eliminating gaseous inclusions, it
may be useful to add chemical fining agents. Such fining agents
fill early-stage bubbles with gas, thus increasing their rise
velocity through the melt. Typical fining agents include, but are
not limited to: oxides of arsenic, antimony, tin and cerium; metal
halides (fluorides, chlorides and bromides); metal sulfates; and
the like. Arsenic oxides are particularly effective fining agents
because they release oxygen very late in the melt stage. However,
arsenic and antimony are generally regarded as hazardous materials.
Accordingly, in one embodiment, the glass is substantially free of
antimony and arsenic, comprising less that about 0.05 wt % of each
of the oxides of these elements. Therefore, it may be advantageous
in particular applications to avoid using arsenic or antimony at
all, and using instead a nontoxic component such as tin, halides,
or sulfates to produce a fining effect. Tin (IV) oxide (SnO.sub.2)
and combinations of tin (IV) oxide and halides are particularly
useful as fining agents in the present invention.
The glass described herein is down-drawable; that is, the glass is
capable of being formed into sheets using down-draw methods such
as, but not limited to, fusion draw and slot draw methods that are
known to those skilled in the glass fabrication arts. Such
down-draw processes are used in the large-scale manufacture of
ion-exchangeable flat glass.
The fusion draw process uses a drawing tank that has a channel for
accepting molten glass raw material. The channel has weirs that are
open at the top along the length of the channel on both sides of
the channel. When the channel fills with molten material, the
molten glass overflows the weirs. Due to gravity, the molten glass
flows down the outside surfaces of the drawing tank. These outside
surfaces extend down and inwardly so that they join at an edge
below the drawing tank. The two flowing glass surfaces join at this
edge to fuse and form a single flowing sheet. The fusion draw
method offers the advantage that, since the two glass films flowing
over the channel fuse together, neither outside surface of the
resulting glass sheet comes in contact with any part of the
apparatus. Thus, the surface properties are not affected by such
contact.
The slot draw method is distinct from the fusion draw method. Here
the molten raw material glass is provided to a drawing tank. The
bottom of the drawing tank has an open slot with a nozzle that
extends the length of the slot. The molten glass flows through the
slot/nozzle and is drawn downward as a continuous sheet
therethrough and into an annealing region. Compared to the fusion
draw process, the slot draw process provides a thinner sheet, as
only a single sheet is drawn through the slot, rather than two
sheets being fused together, as in the fusion down-draw
process.
In order to be compatible with down-draw processes, the alkali
aluminosilicate glass described herein has a high liquidus
viscosity. In one embodiment, the liquidus viscosity is at least
130 kilopoise (kpoise) and, in another embodiment, the liquidus
viscosity is at least 250 kpoise.
In one embodiment, the alkali aluminosilicate glass described
herein is substantially free of lithium. As used herein,
"substantially free of lithium" means that lithium is not
intentionally added to the glass or glass raw materials during any
of the processing steps leading to the formation of the alkali
aluminosilicate glass. It is understood that an alkali
aluminosilicate glass or an alkali aluminosilicate glass article
that is substantially free of lithium may inadvertently contain
small amounts of lithium due to contamination. The absence of
lithium reduces poisoning of ion exchange baths, and thus reduces
the need to replenish the salt supply needed to chemically
strengthen the glass. In addition, due to the absence of lithium,
the glass is compatible with continuous unit (CU) melting
technologies such as the down-draw processes described above and
the materials used therein, the latter including both fused
zirconia and alumina refractories and zirconia and alumina
isopipes.
In one embodiment, the glass is strengthened by ion-exchange. As
used herein, the term "ion-exchanged" is understood to mean that
the glass is strengthened by ion exchange processes that are known
to those skilled in the glass fabrication arts. Such ion exchange
processes include, but are not limited to, treating the heated
alkali aluminosilicate glass with a heated solution containing ions
having a larger ionic radius than ions that are present in the
glass surface, thus replacing the smaller ions with the larger
ions. Potassium ions, for example, could replace sodium ions in the
glass. Alternatively, other alkali metal ions having larger atomic
radii, such as rubidium or cesium could replace smaller alkali
metal ions in the glass. Similarly, other alkali metal salts such
as, but not limited to, sulfates, halides, and the like may be used
in the ion exchange process. In one embodiment, the down-drawn
glass is chemically strengthened by placing it a molten salt bath
comprising KNO.sub.3 for a predetermined time period to achieve ion
exchange. In one embodiment, the temperature of the molten salt
bath is about 430.degree. C. and the predetermined time period is
about eight hours.
Down-draw processes produce surfaces that are relatively pristine.
Because the strength of the glass surface is controlled by the
amount and size of surface flaws, a pristine surface that has had
minimal contact has a higher initial strength. When this high
strength glass is then chemically strengthened, the resultant
strength is higher than that of a surface that has been a lapped
and polished. Chemical strengthening or tempering by ion exchange
also increases the resistance of the glass to flaw formation due to
handling. Accordingly, in one embodiment, the down-drawn alkali
aluminosilicate glass has a warpage of less than about 0.5 mm for a
300 mm.times.400 mm sheet. In another embodiment, the warpage is
less than about 0.3 mm.
Surface compressive stress refers to a stress caused by the
substitution during chemical strengthening of an alkali metal ion
contained in a glass surface layer by an alkali metal ion having a
larger ionic radius. In one embodiment potassium ions are
substituted for sodium ions in the surface layer of the glass
described herein. The glass has a surface compressive stress of at
least about 200 MPa. In one embodiment, the surface compressive
stress is at least about 600 MPa. The alkali aluminosilicate glass
has a compressive stress layer that has a depth of at least about
30 .mu.m and, in one embodiment, the depth of the compressive
stress layer is at least about 40 .mu.m.
The replacement of smaller ions by larger ions at a temperature
below that at which the glass network can relax produces a
distribution of ions across the surface of the glass that results
in a stress profile. The larger volume of the incoming ion produces
compressive stress (CS) on the surface and tension in the center
(CT) of the glass. The compressive stress is related to the central
tension by the following relationship: CS=CT.times.(t-2DOL)/DOL;
where t is the thickness of the glass and DOL is the depth of
exchange.
A lithium-free glass having a surface compressive stress of at
least about 200 MPa, a surface compressive layer having a depth of
at least about 30 .mu.m, and a thickness of at least about 0.3 mm
is also provided. In one embodiment, the compressive stress is at
least about 600 MPa, the depth of the compressive layer is at least
about 40 .mu.m, and the thickness of the lithium-free glass is in a
range from about 0.7 mm up to about 1.1 mm.
In one embodiment, the lithium-free glass comprises: 64 mol
%.ltoreq.SiO.sub.2.ltoreq.68 mol %; 12 mol
%.ltoreq.Na.sub.2O.ltoreq.16 mol %; 8 mol
%.ltoreq.Al.sub.2O.sub.3.ltoreq.12 mol %; 0 mol
%.ltoreq.B.sub.2O.sub.3.ltoreq.3 mol %; 2 mol
%.ltoreq.K.sub.2O.ltoreq.5 mol %; 4 mol %.ltoreq.MgO.ltoreq.6 mol
%; and 0 mol %.ltoreq.CaO.ltoreq.5 mol %, wherein: 66 mol
%.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol %;
Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %, and
has a liquidus viscosity of at least 130 kpoise. The liquidus
viscosity in one embodiment is at least 250 kpoise.
A mobile electronic device comprising a cover plate, at least a
portion of which is transparent, is also provided. Such mobile
electronic devices include, but are not limited to, mobile
communication devices such as personal data assistants, mobile
telephones, pagers, watches, radios, laptop computers and
notebooks, and the like. As used herein, a "cover plate" refers to
a glass sheet or window that covers a visual display. At least a
portion of the cover plate is transparent to allow viewing of the
display. The cover plate may to some extent be resistant to shock,
breakage, and scratching and finds application in those electronic
devices where a window having high surface strength, hardness, and
scratch resistance is desirable. In one embodiment, the cover plate
is touch sensitive. A schematic representation of a top view of a
mobile telephone is shown in FIG. 1. Mobile telephone 100 includes
a cover plate 110 comprising the down-drawn alkali aluminosilicate
and chemically strengthened glass described herein. In mobile
telephone 100, cover plate 110 serves as a display window and is
scratch resistant. Cover plate 110 is formed from any of the
glasses described herein. A sheet of the glass is down-drawn and
then cut to the desired shape and size of the cover plate. The
glass sheet may, in one embodiment, be strengthened by ion
exchange, as described herein. In one embodiment, the glass sheet
and cover plate cut therefrom have a thickness ranging from about
0.3 mm up to and including about 3 mm. In another embodiment, the
glass sheet and cover plate have a thickness ranging from about 0.3
mm up to and including about 1.5 mm. The cover plate may then be
joined to the body of the mobile electronic device using an
adhesive or other means known in the art.
A cover plate for a device such as, but not limited to, the mobile
electronic devices described above as well as non-electronic
watches and other like, is also provided. The cover plate is formed
from any of the glasses described herein above.
The following examples illustrate the advantages and features of
the invention and in are no way intended to limit the invention
thereto.
EXAMPLE 1
Melting of a Glass of from Raw Materials
The following describes a method for making a glass having a
nominal composition equivalent to Example 29 in Table 1. The
following materials are mixed together in the masses indicated
(quantities in grams):
TABLE-US-00003 Silica sand, -200 mesh 1224.42 Alumina, 325 mesh
322.21 Boric acid 24.12 Soda ash 452.95 Potassium carbonate 104.78
Magnesia 74.02 Limestone 15.78 Arsenic pentoxide 28.41
For various melting operations, it may be desirable to use coarser
or finer alumina or silica; hydroxides of alumina, alkali metals,
or alkaline earth metals; oxides, peroxides or superoxides of the
alkali metals; peroxides of the alkaline earth metals; or
carboxylates of the alkali or alkaline earth metals. Arsenic is
present only as a fining agent, and adds nothing to the physical
properties or ion exchange capability of the glass. Arsenic acid
can be used instead of arsenic pentoxide. Alternatively, if gaseous
inclusions can be avoided by other means such as, for example,
vacuum fining or long residence time in a refining stage of
melting, it may be acceptable to reduce or eliminate arsenic oxide,
to replace it with antimony or tin oxide, or to eschew all these in
favor of halide or sulfate raw materials to provide additional
fining capacity.
The raw materials are mixed by vigorously shaking or stirring the
materials together. If soft agglomerates are present, a more
aggressive mixing method such as ball-milling may be appropriate.
The well-mixed batch is transferred into a 1800 cm.sup.3 platinum
crucible contained within a refractory backer, and the crucible
containing the batch and the backer are loaded into a furnace,
heated at a temperature in a range from about 1575.degree. C. up to
and including about 1650.degree. C., and held at temperature for 4
to 16 hours. After this time, the crucible is removed from the
furnace and the glass is poured into a free-forming patty of glass
on a cold steel plate, and then transferred to an annealing oven at
625.degree. C. After 2 hours at temperature, the annealing oven is
ramped to room temperature (about 25.degree. C.) at a rate of about
2.degree. C. per minute, after which time the glass is removed and
subjected to further processing.
EXAMPLE 2
Ion Exchange of Glass Plates
The following example describes sample preparation and ion exchange
experiments. A glass patty such as that made in Example 1 is cut
into shapes suitable for ion exchange evaluation. For the purposes
of this example, the preferred sample geometry for consistent
comparison of different glasses is 1 mm thick by 5 mm wide by 40 mm
in length, although in other applications, a larger or smaller
sample may be desired. The sample is ground to appropriate
dimensions and then given an optical polish on all surfaces. The
samples are then cleaned in methyl ethyl ketone and dried at about
150.degree. C. for 1 hour to eliminate any residual organic
contamination. Each cleaned sample is suspended in a bath of molten
KNO.sub.3 and held at 430.degree. C. so as to minimize points of
contact between the glass and the holder or bath vessel. Other
alkali salts, such as nitrates and halides of K, Rb, and Cs, may
also be used. After eight hours in the bath, the sample is removed,
allowed to cool, and washed in deionized water to remove any
residual salt.
While typical embodiments have been set forth for the purpose of
illustration, the foregoing description should not be deemed to be
a limitation on the scope of the invention. Accordingly, various
modifications, adaptations, and alternatives may occur to one
skilled in the art without departing from the spirit and scope of
the present invention.
* * * * *